JP2014053358A - Wafer processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wafer processing method capable of reducing the possibility that the height of bumps varies and electric connection becomes unstable.SOLUTION: A wafer processing method comprises: an embedded electrode detection step of detecting depths of tips of a plurality of embedded electrodes from a rear surface of a wafer; and a rear surface grinding step of thinning the wafer by grinding the rear surface of the wafer to such an extent that the embedded electrodes are not exposed to the rear surface after performing the embedded electrode detection step. The rear surface grinding step further includes: a rough grinding step of roughly grinding the rear surface of the wafer; a chuck table cleaning step of detecting presence or absence of a dimple in the wafer after performing the rough grinding step; cleaning a holding surface 36a of a chuck table 20 when a dimple is detected in the wafer; and finish-grinding step of finish-grinding the roughly ground rear surface after performing the chuck table cleaning step or when a dimple is not detected in the wafer.

Description

  The present invention relates to a method for processing a wafer such as a semiconductor wafer.

  In recent years, in order to achieve high integration, high density, miniaturization, and thinning of semiconductor devices, a stacked type in which a plurality of semiconductor chips such as MCP (multi-chip package) and SIP (system in package) are stacked. Semiconductor packages have been proposed.

  Such a stacked semiconductor package is formed by stacking a plurality of semiconductor chips on a package substrate called an interposer. In general, the interposer and the semiconductor chip electrodes, or the electrodes of the stacked semiconductor chips are electrically connected with a gold wire, and then the semiconductor chip is molded and sealed with resin to the interposer. A semiconductor package is manufactured.

  However, in this method, since the gold wire bonded to the electrode of the semiconductor chip protrudes to the outer peripheral surplus region of the semiconductor chip, there is a problem that the package size becomes larger than the semiconductor chip.

  In addition, when the mold is sealed with the resin, the wire wire is deformed to cause a disconnection or a short circuit, or the air remaining in the mold resin expands upon heating and causes damage to the semiconductor package. .

  Therefore, a technique of providing a through electrode (via electrode) that penetrates the semiconductor chip in the thickness direction and connects to the electrode of the semiconductor chip in the semiconductor chip, stacking the semiconductor chips and joining the through electrodes and electrically connecting the electrodes. Has been proposed (see, for example, Japanese Patent Application Laid-Open Nos. 2004-207606 and 2005-136187).

  In this method, a plurality of semiconductor devices are formed on the surface of the silicon wafer, and from each semiconductor device, a plurality of embedded copper electrodes (copper posts) that are connected to the electrodes of the semiconductor device and extend to the back side of the silicon wafer are formed. A so-called TSV (Through Silicon Via) wafer is used.

  The embedded copper electrode has a height equal to or higher than the finished thickness of the semiconductor chip, and the back surface of the wafer is ground and polished by a grinding device to thin the wafer to a thickness just before the embedded copper electrode is exposed from the back surface. Thereafter, by selectively etching only the silicon wafer, the tip of the buried copper electrode protrudes from the back surface of the wafer to form a through electrode.

  After etching the back surface of the wafer to make the tip of the embedded copper electrode protrude from the back surface to form a through electrode, an insulating film coating step is performed to cover the back surface of the wafer with an insulating film, and then the insulating film at the end of the through electrode After the bumps are formed by removing the wafer, the wafer is divided into individual chips (devices) to form chips (devices) having bumps at both ends of the through electrodes.

JP 2004-207606 A JP 2005-136187 A

  The wafer processing method as described above includes a number of processes, and in particular, when a metal bump is attached to the through electrode penetrating to the back surface, a predetermined flatness is required on the exposed upper surface of the through electrode. Is done. Further, if the semiconductor wafer is not formed with a uniform height, the height of the mounted bumps varies, and the electrical connection becomes unstable.

  The present invention has been made in view of the above, and an object of the present invention is to provide a wafer processing method capable of reducing the possibility that the height of bumps varies and the electrical connection becomes unstable. It is.

  According to the present invention, a plurality of embedded electrodes each having a device formed in each region partitioned by a plurality of scheduled division lines formed in a lattice pattern on the surface and reaching a depth equal to or greater than the finished thickness of the wafer. Is a wafer processing method in which a wafer having a chamfered portion on the outer peripheral edge is divided into individual devices, and a cutting blade is positioned on the outer peripheral edge of the wafer so that the wafer has a circular shape with a predetermined depth from the surface side. A chamfered portion removing step for cutting and partially removing the chamfered portion, a carrier plate arranging step for arranging a carrier plate on the wafer surface via a resin after performing the chamfered portion removing step, and the carrier plate After performing the arranging step, the embedded electrode detecting step for detecting the depths of the tips of the plurality of embedded electrodes from the back surface of the wafer; After performing the embedded electrode detection process, the back surface grinding process for grinding and thinning the back surface of the wafer to such an extent that the embedded electrode is not exposed on the back surface, and after performing the back surface grinding process, etching the wafer from the back surface of the wafer An etching process in which the embedded electrode protrudes from the back surface of the wafer to form a through electrode, an insulating film coating process for covering the back surface of the wafer with an insulating film after the etching process is performed, and the insulating film coating process. After performing the finishing step of removing the through electrode protruding from the back surface of the wafer and exposing it from the insulating film and finishing the head of the through electrode on the same surface as the insulating film, and after performing the finishing step, A bump disposing step of disposing a bump on the head of each through electrode, and after performing the bump disposing step, a dicing tape is attached to the back surface of the wafer and A transfer step of removing the carrier plate from the front surface of the wafer and transferring the wafer to the dicing tape; and a dividing step of dividing the wafer into individual devices after the transfer step is performed. The grinding process includes a rough grinding process for rough grinding the back surface of the wafer, a dimple presence / absence detection process for detecting the presence / absence of dimples on the wafer after the rough grinding process, and when the dimples are detected on the wafer, A chuck table cleaning process for cleaning the holding surface; and a finish grinding process for finishing grinding the rough ground back surface after the chuck table cleaning process is performed or when dimples are not detected on the wafer. A method for processing a wafer is provided.

  According to the wafer processing method of the present invention, the dimple presence / absence detection step is performed after the wafer is roughly ground, and when the dimple is detected, the chuck table cleaning step is performed to clean the holding surface of the chuck table.

  Therefore, it is possible to prevent dimples from occurring in a new wafer after the chuck table cleaning process has been performed, so that it is possible to reduce the wafer thickness variation, and the bump height varies and the electrical connection becomes unstable. Can be reduced.

FIG. 1A is a front perspective view of a semiconductor wafer having a buried copper electrode with bumps, and FIG. 1B is a cross-sectional view thereof. It is a partial cross section side view which shows a chamfer part removal process. It is sectional drawing of the semiconductor wafer after a chamfer part removal process implementation. It is sectional drawing explaining a carrier plate arrangement | positioning process. It is sectional drawing which shows an embedded copper electrode detection process. It is a partial cross section side surface which shows the rough grinding process in a back surface grinding process. It is sectional drawing which shows the thickness variation measurement process of a wafer. It is a partial cross section side view which shows a chuck | zipper table washing | cleaning process. It is a position section side view showing the finish grinding process in the back grinding process. It is sectional drawing of the wafer after back surface grinding process implementation. It is sectional drawing of the wafer after an etching process implementation. It is sectional drawing of the wafer after insulating film coating process implementation. It is a partial cross section side view which shows a finishing process. It is sectional drawing of the wafer after finishing process implementation. It is sectional drawing of the wafer after bump provision process implementation. It is sectional drawing explaining a transfer process. It is a partial cross section side view which shows a division | segmentation process.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Referring to FIG. 1A, a perspective view of a semiconductor wafer 11 having a buried electrode with bumps to be processed by the processing method of the present invention is shown. FIG. 1B is a longitudinal sectional view thereof. The buried copper electrode is made of a conductive material, for example, copper.

  A semiconductor wafer 11 shown in FIG. 1 is made of, for example, a silicon wafer having a thickness of 700 μm, and a plurality of division lines (streets) 13 are formed in a lattice shape on the surface 11a, and a plurality of division lines 13 are formed. A device 15 such as an IC or an LSI is formed in each of the areas partitioned by.

  As shown in FIG. 1B, from each semiconductor device 15 formed on the semiconductor wafer 11, a plurality of embedded copper electrodes 21 embedded at a depth equal to or larger than the finished thickness t1 of the device extend toward the back surface 11b. ing. A bump 23 is bonded to the upper end of each embedded electrode 21.

  As shown in FIG. 1 (A), the semiconductor wafer 11 thus configured (hereinafter sometimes simply referred to as a wafer) 11 includes a device region 17 in which a plurality of semiconductor devices 15 are formed, An outer peripheral surplus area 19 surrounding the device area 17 is provided on the surface 11a. Further, as shown in FIG. 1B, an arc-shaped chamfered portion 11 e is formed on the outer peripheral portion of the wafer 11.

  In the wafer processing method of the present invention, first, a chamfered portion removing step for removing the chamfered portion 11e of the wafer 11 is performed. In this chamfered portion removing step, as shown in FIG. 2, the wafer 11 is sucked and held by the chuck table 10 of the cutting apparatus.

  In FIG. 2, reference numeral 12 denotes a cutting unit of a cutting apparatus. A spindle 16 is rotatably supported in a spindle housing 14, and a cutting blade 18 is attached to the tip of the spindle 16.

  In this chamfered portion removing step, the cutting blade 18 of the cutting unit 12 rotating at high speed is cut into the chamfered portion 11e of the wafer 11 by a predetermined depth from the surface 11a side, and the chuck table 10 is rotated at a low speed, as shown in FIG. As described above, a circular step portion 11 f is formed on the outer peripheral portion of the wafer 11.

  The cutting depth of the cutting blade 18 in this chamfered portion removing step is at least the depth from the surface 11a of the wafer 11 to the finished thickness of the wafer 11, and forms a circular step portion 11f having a depth of about 100 μm, for example. As the cutting blade 18, for example, a washer blade having a thickness of about 1 to 2 mm is preferably used.

  The chamfered portion removing step shown in FIG. 2 is performed by cutting the cutting blade 18 into the chamfered portion 11e of the wafer 11, and grinding is performed by bringing a grinding wheel into contact with the chamfered portion 11e of the wafer 11 on the grinding wheel. Thus, a part of the chamfered portion 11e may be removed.

  A cross-sectional view of the wafer 11 after the chamfered portion removing step is shown in FIG. The circular step portion 11f is at least a depth from the surface 11a of the wafer 11 to the finished thickness of the wafer 11, and has a depth of about 100 μm from the surface 11a of the wafer 11, for example.

  After performing the chamfered portion removing step, as shown in FIG. 4, a carrier plate disposing step of disposing the carrier plate 25 on the surface 11a of the wafer 11 via the resin 27 having adhesiveness is performed. The resin 27 acts as an adhesive, and the carrier plate 25 is adhered to the surface 11 a of the wafer 11 with the resin 27.

  The carrier plate 25 is made of, for example, a silicon wafer having a uniform thickness or glass. In the present embodiment, the carrier plate 25 is illustrated as being formed of glass. The thickness of the resin 27 is preferably about 20 μm, for example.

  After the carrier plate placement step, a buried copper electrode detection step for detecting the depth of the tip of the buried copper electrode 21 from the back surface 11b of the wafer 11 is performed. In this embedded copper electrode detection step, for example, as shown in FIG. 5, the carrier plate 25 is sucked and held by the chuck table 20 of the grinding apparatus, and the wafer 11 is imaged from the back surface 11b side by the infrared camera (IR camera) 22. To implement.

  Since infrared rays pass through the silicon wafer 11, the focal point of the IR camera 22 is changed to focus on the front surface 11a of the wafer 11, the tip of the embedded copper electrode 21, and the back surface 11b of the wafer 11 to detect the focal length. Thus, the height of the front surface 11a of the wafer 11, the front end of the embedded copper electrode 21 and the back surface 11b of the wafer 11 can be detected, and the depth of the front end of the embedded copper electrode 21 from the back surface 11b of the wafer can be detected. it can.

  The wafer 11 is imaged while moving the IR camera 21 in the direction of arrow A, the depths of all the embedded copper electrodes 21 are detected, and the detected values are stored in a memory provided in the controller of the grinding apparatus.

  After performing the embedded copper electrode detection process, a back surface grinding process is performed in which the back surface 11b of the wafer 11 is ground and thinned so that the embedded copper electrode 21 is not exposed on the back surface 11b of the wafer 11. In this back surface grinding step, as shown in FIG. 6, the carrier plate 25 is sucked and held by the chuck table 20 of the grinding device, and the back surface 11b of the wafer 11 is exposed.

  In FIG. 6, the rough grinding unit 24 of the grinding apparatus includes a spindle 26 that is rotationally driven by a motor (not shown), a wheel mount 28 that is fixed to the tip of the spindle 26, and a rough grinding that is detachably attached to the wheel mount 28. Wheel 30. The rough grinding wheel 30 includes an annular wheel base 32 and a plurality of rough grinding wheels 34 fixed to the outer periphery of the lower end of the wheel base 32.

  In this back grinding process, while rotating the chuck table 20 in the direction indicated by the arrow a at 300 rpm, for example, the rough grinding wheel 30 is rotated in the direction indicated by the arrow b at, for example, 6000 rpm, and a grinding unit feed mechanism (not shown) is driven. Then, the rough grinding wheel 34 of the rough grinding wheel 30 is brought into contact with the back surface 11 b of the wafer 11.

  Then, the rough grinding wheel 30 is ground and fed downward by a predetermined amount at a predetermined grinding feed speed. While measuring the thickness of the wafer 11 with a contact-type or non-contact-type thickness measurement gauge, the wafer 11 is ground to a thickness just before the tip of the embedded copper electrode 21 is exposed on the back surface 11b of the wafer 11 as shown in FIG. To do.

  After the rough grinding process in the back grinding process, a dimple presence / absence detection process is performed. In the present embodiment, as shown in FIG. 7, the thickness of the wafer 11 is measured while scanning a non-contact type thickness measuring device 38 in the direction of arrow A, and a local thickness variation of the wafer is detected.

  When a locally thinned portion is detected, a dimple is formed by inserting foreign matter such as grinding dust between the holding surface 36a of the suction holding portion 36 of the chuck table 20 and the carrier plate 25. It is thought that it was done. Therefore, when the wafer 11 is removed from the chuck table 20, dimples are formed on the back surface 11b of the wafer 11 corresponding to the portion where the foreign object has been caught.

  As described above, the thickness variation of the wafer 11 is detected to detect a portion where the wafer thickness is locally thin as dimples, and an image formed by imaging the surface to be ground of the wafer 11 after the rough grinding process is performed. Originally, the presence or absence of dimples may be detected.

  In the processing method of the present invention, when dimples are detected on the wafer 11, the wafer 11 supported by the carrier plate 25 is removed from the chuck table 20, and the cleaning liquid 41 is supplied from the cleaning liquid supply nozzle 40 as shown in FIG. 8. The chuck table 20 is supplied to the holding surface 36a.

  Since the foreign matter on the holding surface 36 is removed by this chuck table cleaning process, even if dimples are formed on the wafer 11, the dimples can be removed by grinding the wafer 11 in the subsequent grinding process.

  After performing the chuck table cleaning process, a finish grinding process for finish grinding the back surface 11b of the wafer 11 is performed. In the finish grinding step, the chuck table 20 holding the wafer 11 is positioned in a finish grinding region by the finish grinding unit 42 as shown in FIG.

  In FIG. 9, the finish grinding unit 42 includes a spindle 44 that is rotationally driven by a motor (not shown), a wheel mount 46 that is fixed to the tip of the spindle 44, and a finish grinding wheel 48 that is detachably attached to the wheel mount 46. Is included. The finish grinding wheel 48 includes an annular wheel base 50 and a plurality of finish grinding wheels 52 fixed to the outer periphery of the lower end of the wheel base 50.

  In the finish grinding process, while rotating the chuck table 20 in the direction indicated by the arrow a at 300 rpm, for example, the grinding wheel 48 is rotated in the direction indicated by the arrow b at, for example, 6000 rpm, and the grinding unit feed mechanism (not shown) is driven to finish. The grinding wheel 52 of the grinding wheel 48 is brought into contact with the back surface 11 b of the wafer 11.

  Then, the finish grinding wheel 48 is ground and fed by a predetermined amount at a predetermined grinding feed speed to grind the wafer 11 to 2 to 3 μm, and the wafer is brought to a thickness just before the tip of the embedded copper electrode 21 is exposed on the back surface 11b of the wafer 11. 11 is finish ground.

  After the back surface grinding step, the wafer 11 is selectively etched from the back surface 11b of the wafer 11, and as shown in FIG. 11, the embedded copper electrode 21 protrudes from the back surface 11b of the wafer 11 to form a through electrode. carry out. This etching step is preferably performed by plasma etching, for example.

  After performing the etching process, as shown in FIG. 12, an insulating film coating process for coating the back surface 11b of the wafer 11 with the insulating film 29 is performed. By this insulating film coating step, the insulating film 29 is coated not only on the back surface 11 b of the wafer 11 but also on the tip surface of the through electrode 21.

  After performing the insulating film coating step, the portion of the through electrode 21 protruding from the back surface 11 b of the wafer 11 is removed to expose the through electrode 21 from the insulating film 29 and finish the head of the through electrode 21 on the same surface as the insulating film 29. Perform the process.

  In the present embodiment, this finishing step is performed using a bite wheel 62 of a bite cutting device as shown in FIG. The cutting tool unit 56 of the cutting tool includes a spindle 58 that is rotationally driven by a motor (not shown), a wheel mount 60 that is fixed to the tip of the spindle 58, and a cutting tool wheel 62 that is detachably attached to the wheel mount 60. Contains. The bite wheel 62 includes an annular wheel base 64 and a bite tool 66 having a cutting edge 66 a attached to the outer periphery of the lower end of the wheel base 64.

  In cutting the wafer 11 held on the chuck table 54, a cutting tool 66 feed mechanism (not shown) is driven while rotating the cutting tool wheel 62 in the direction of arrow R at about 2000 rpm, and the cutting blade 66a of the cutting tool 66 is passed through the through electrode. The insulating film 29 covered with 21 is cut into a predetermined depth.

  Then, while the chuck table 54 is linearly moved in the direction of arrow A at a feed rate of, for example, 1 mm / s, the through electrode 21 protruding from the upper surface of the wafer 11 is turned and cut together with the insulating film 29. During this turning cutting, the chuck table 54 is processed and fed in the direction of arrow A without rotating.

  As shown in FIG. 14, the turning electrode 21 is exposed from the insulating film 29 and the head of the penetrating electrode 21 is finished on the same surface as the insulating film 29 covered with the surface 11 a of the wafer 11.

  When the head of the through electrode 21 cannot be finished on the same surface as the insulating film 29 by one turn cutting, the cutting depth is adjusted and the turning cutting is performed a plurality of times to expose the through electrode 21 from the insulating film 29. In addition, the head of the through electrode 21 is finished on the same surface as the insulating film 29.

  In the finishing process using the cutting tool 66 of the above-described embodiment, the projecting portions of the through electrodes 21 that are dispersed and arranged by the cutting blades 66a of the cutting tool 66 are swiveled together with the insulating film 29. Before the implementation, the surface of the insulating film 29 may be covered with a resin layer, and the protruding portion of the through electrode 21 may be turned and cut together with the resin layer.

  By providing the resin layer on the surface of the insulating film 29 in this manner, the cutting edge 66a of the cutting tool 66 always turns and cuts the resin layer by eliminating the protrusion on the surface to be cut of the wafer. The load can be made uniform to some extent.

  The finishing process is not limited to the cutting with the above-described cutting tool 66, and may be performed by grinding with a grinding wheel. Alternatively, the protruding portion of the through electrode 21 may be selectively polished by CMP to finish the head of the through electrode 21 on the same surface as the insulating film 29.

  After performing the finishing process using the bite wheel 62, as shown in FIG. 15, a bump disposing process for disposing the bump 31 on the head of the through electrode 21 is performed. The bump 31 is made of, for example, solder, and the bump 31 made of solder is joined to the head of the through electrode 21.

  After the bump placement step, as shown in FIG. 16, the dicing tape T is adhered to the back surface 11b of the wafer 11, the carrier plate 25 is removed from the front surface 11a of the wafer 11, and the wafer 11 is transferred to the dicing tape T. Perform the transfer process. The outer peripheral portion of the dicing tape T is attached to the annular frame F. As a result, the wafer 11 is supported by the annular frame F via the dicing tape T.

  Next, for example, the wafer 11 is sucked and held via the dicing tape T by a chuck table of a cutting device (not shown), and the wafer is removed by a cutting blade 74 attached to the tip of the spindle 72 of the cutting unit 70 as shown in FIG. 11 is cut along the planned division line 13 until reaching the dicing tape T, and a division pre-process for dividing the wafer 11 into individual devices 15 is performed. Each device 15 includes a plurality of through electrodes 21 having bumps 23 and 31 bonded to both ends.

  The dividing step may be performed by laser processing using a laser processing apparatus instead of cutting by the cutting blade 74. In this laser processing, a laser beam having a wavelength that absorbs the wafer is irradiated, laser processing grooves are formed along the division lines 13 by ablation processing, and then an external force is applied to the wafer to individually handle the wafer. A method of dividing the wafer into the devices 15 or irradiating a laser beam having a wavelength transmissive to the wafer to form a modified layer inside the wafer, and then applying an external force to the wafer to use the modified layer as a dividing starting point. Any method of dividing the wafer into the individual devices 15 may be used.

  According to the wafer processing method of the embodiment described above, it is detected whether or not the dimples are formed after the rough grinding of the wafer. When dimples are detected, a case in which foreign matter is caught between the holding surface 36a of the chuck table 20 and the carrier plate 25 can be considered. Therefore, a chuck table cleaning process for cleaning the holding surface 36a of the chuck table 20 is possible. To implement.

  Therefore, in a newly ground wafer, it is possible to prevent the occurrence of dimples due to foreign matters, and the dimples are removed by the finish grinding performed after the cleaning process even in the wafer on which the dimples are formed. Therefore, it is possible to suppress the wafer thickness variation and reduce the possibility that the bump height varies and the electrical connection becomes unstable.

11 Semiconductor Wafer 11e Chamfer 13 Divided Line 15 Device 18 Cutting Blade 21 Embedded Copper Electrode (Penetration Electrode)
22 IR camera 23, 31 Bump 25 Carrier plate 29 Insulating film 30 Coarse grinding wheel 34 Coarse grinding wheel 38 Non-contact type thickness measuring instrument 40 Cleaning liquid supply nozzle 42 Finish grinding unit 48 Finish grinding wheel 62 Byte wheel 66 Byte tool 66a Cutting blade 74 Cutting blade T Dicing tape F Annular frame

Claims (1)

A device is formed in each region partitioned by a plurality of division lines formed in a lattice pattern on the surface, and a plurality of embedded electrodes extending from each device to a depth greater than the finished thickness of the wafer are embedded. A wafer processing method for dividing a wafer having a chamfered portion on the outer peripheral edge into individual devices,
A chamfered portion removing step in which a cutting blade is positioned on the outer peripheral edge of the wafer, the wafer is cut into a circular shape of a predetermined depth from the surface side, and the chamfered portion is partially removed;
A carrier plate disposing step of disposing a carrier plate via a resin on the surface of the wafer after performing the chamfered portion removing step;
After performing the carrier plate placement step, embedded electrode detection step of detecting the depth of the tip of the plurality of embedded electrodes from the back surface of the wafer;
After performing the embedded electrode detection step, a back surface grinding step of grinding and thinning the back surface of the wafer to such an extent that the embedded electrode is not exposed on the back surface;
After performing the back surface grinding step, etching the wafer from the back surface of the wafer to etch the embedded electrode from the back surface of the wafer to be a through electrode, and
After performing the etching step, an insulating film coating step of coating an insulating film on the back surface of the wafer;
After performing the insulating film coating step, the through electrode protruding from the back surface of the wafer is removed and exposed from the insulating film, and the finishing step of finishing the head of the through electrode on the same surface as the insulating film;
After performing the finishing step, a bump disposing step of disposing a bump on the head of each through electrode;
After carrying out the bump arranging step, a dicing tape is attached to the back surface of the wafer and the carrier plate is removed from the front surface of the wafer, and a transferring step for transferring the wafer to the dicing tape;
Dividing the wafer into individual devices after performing the transfer step, and
The back grinding step is a rough grinding step of rough grinding the back surface of the wafer;
A dimple presence / absence detection step for detecting the presence / absence of dimples on the wafer after the rough grinding step;
A chuck table cleaning step for cleaning the holding surface of the chuck table when dimples are detected in the wafer;
After the chuck table cleaning step or when dimples are not detected on the wafer, a finish grinding step of finish grinding the back surface subjected to rough grinding;
A method for processing a wafer, comprising:

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